A diacritic is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek διακριτικός, from διακρίνω. The word diacritic is a noun, though it is sometimes used in an attributive sense, whereas diacritical is only an adjective. Some diacritics, such as the acute ⟨á⟩, grave ⟨à⟩, and circumflex ⟨â⟩, are often called accents. Diacritics may appear above or below a letter or in some other position such as within the letter or between two letters.

Hanyu Pinyin, or simply pinyin, is the most common romanization system for Standard Chinese. In official documents, it is referred to as the Chinese Phonetic Alphabet. It is the official system used in China, Singapore, Taiwan, and by the United Nations. Its use has become common when transliterating Standard Chinese mostly regardless of region, though it is less ubiquitous in Taiwan. It is used to teach Standard Chinese, normally written with Chinese characters, to students already familiar with the Latin alphabet. The system makes use of diacritics to indicate the four tones found in Standard Chinese, though these are often omitted in various contexts, such as when spelling Chinese names in non-Chinese texts, or when writing non-Chinese words in Chinese-language texts. Pinyin is also used by various input methods on computers and to categorize entries in some Chinese dictionaries. Hànyǔ literally means 'Han language'—meaning, the Chinese language—while pinyin literally means 'spelled sounds'.